Functional Sugar Beet Pectin

Pectin is widely regarded as a natural material and there is increasing evidence for useful bioactive properties of pectin. Traditionally pectin is extracted from the solid residue left after juice extraction in the cider and citrus fruits industries and is used as a gelling agent for the food industry. Pectin extracted from sugar beet pulp, a byproduct of the production of sugar from sugar beet, is unusual in that it can be used to stabilise food emulsions. Food emulsions are produced by generating and stabilising droplets of oil in water or water in oil. The stabilisation is achieved through the structures formed when molecules (emulsifiers) adsorb at the interfaces between the oil and the water. Carbohydrates such as pectin are normally poor emulsifiers, but sugar beet pectin is known to contain protein which is believed to account for its ability to act as an emulsifier. By using novel microscopic techniques that can visualise molecules we have identified the presence of protein-pectin complexes in sugar beet pectin extracts. This new knowledge allows us to suggest and test mechanisms by which beet pectin extracts can stabilise emulsions. It also suggests ways in which the properties of the beet pectin extracts could be rationally improved to enhance their commercial value. The imminent cut in the EU subsidy for sugar beet also provides an incentive for improving or generating new commercial uses for beet pectin in order to help sustain production of this crop in the UK, particularly in the East Anglia region. Currently the main carbohydrate-based food emulsifier is gum Arabic. This is imported from Africa and political and environmental uncertainties can threaten stability of cost and supply. Sugar beet pectin extracts offer a UK alternative with stable cost and supply.

Extracts of sugar beet pectin are unusual in that they act as emulsifiers. Beet pectin extracts generally contain significant levels of protein and it has been suggested that the protein content is responsible for the behaviour as an emulsifier. As demonstrated in this grant proposal we have been able to image, for the first time, protein-pectin complexes in beet pectin extracts. The complexes have a distinctive tadpole-like appearance, with the protein apparently attached specifically to one end of the pectin molecule. This new information allows us to formulate testable hypotheses on the mode of action of beet pectin extracts at oil-water interfaces and on how to rationally improve and manipulate its behaviour. The hypotheses to be tested are: 1. That pectin/protein complexes are key to emulsification by beet pectin. 2. That the protein components of these complexes adsorb, partially unfold and form elastic networks at the oil/water interface. 3. That the pectin chains extend out from the oil droplets into the aqueous phase sterically preventing droplet coalescence. 4. That the pectin structure can be rationally modified enzymatically to induce and control bridging flocculation of oil droplets. These hypotheses will be tested by:- 1. Direct characterisation of the interfacial behaviour of purified sugar beet pectin samples.To show that beet pectin extracts adsorb at interfaces. 2. Observation for the first time of the structure of interfacial layers formed by beet pectin extracts at the oil/water interface. To assess roles of (tadpoles)complexes. 3. The first direct measurements of potential steric repulsions between oil droplets due to adsorbed beet pectin extracts. To show that the polysaccharide chains influence droplet-droplet interactions. 4. The first direct measurements of potential adhesion between pectin polysaccharide layers on oil droplets induced by bridging effects. To show that this interaction can be rationally modified.